The present invention relates to resilient (spring) electrical contact (interconnection) elements (structures) suitable for but not limited to effecting pressure connections between electronic components and, more particularly, to microminiature spring contacts such as may be used in probing (resiliently and temporarily contacting) microelectronic components such as active semiconductor devices.
Commonly-owned U.S. Pat. No. 4,576,211, and related U.S. Pat. Nos. 6,049,976 and 5,852,871, disclose methods for making resilient interconnection elements for microelectronics applications involving mounting an end of a flexible elongate core element (e.g., wire xe2x80x9cstemxe2x80x9d or xe2x80x9cskeletonxe2x80x9d) to a terminal on an electronic component, and coating the flexible core element and adjacent surface of the terminal with a xe2x80x9cshellxe2x80x9d of one or more materials having a predetermined combination of thickness, yield strength and elastic modulus to ensure predetermined force-to-deflection characteristics of the resulting spring contacts. Exemplary materials for the core element include gold. Exemplary materials for the coating include nickel and its alloys. The resulting spring contact element is suitably used to effect pressure, or demountable, connections between two or more electronic components, including semiconductor devices.
Commonly-owned U.S. Pat. No. 5,917,707 discloses a number of applications for the aforementioned spring contact element, and techniques for fabricating contact pads at the ends of the spring contact elements. For example, in FIG. 14 thereof, a plurality of negative projections or holes, which may be in the form of inverted pyramids ending in apexes, are formed in the surface of a sacrificial layer (substrate). These holes are then filled with a contact structure comprising layers of material such as gold or rhodium and nickel. A flexible elongate element is mounted to the resulting contact structure and can be overcoated in the manner described hereinabove. In a final step, the sacrificial substrate is removed. The resulting spring contact has a contact pad having controlled geometry (e.g., sharp points) at its free end.
Commonly-owned U.S. Pat. No. 6,336,269 discloses additional techniques and metallurgies for fabricating contact tip structures on sacrificial substrates, as well as techniques for transferring a plurality of spring contact elements mounted thereto, en masse, to terminals of an electronic component (see, e.g., FIGS. 11A-11F and 12A-12C therein).
Commonly-owned U.S. No. 5,994,152 discloses techniques whereby a plurality of contact tip structures (see, e.g., #620 in FIG. 6B therein) are joined to a corresponding plurality of elongate contact elements (see, e.g., #632 of FIG. 6D therein) which are already mounted to an electronic component (#630). This patent application also discloses, for example in FIGS. 7A-7E therein, techniques for fabricating xe2x80x9celongatexe2x80x9d contact tip structures in the form of cantilevers. The cantilever tip structures can be tapered, between one end thereof and an opposite end thereof. The cantilever tip structures of this patent application are suitable for mounting to already-existing (i.e., previously fabricated) raised interconnection elements (see, e.g., #730 in FIG. 7F) extending (e.g., free-standing) from corresponding terminals of an electronic component (see. e.g., #734 in FIG. 7F).
WIPO Publication No. WO97/43653, published Nov. 20, 1997, which is incorporated by reference herein, discloses a number of processes and metallurgies for prefabricating contact tip structures on sacrificial substrates, for later joining to ends of spring contact elements, as well as mechanisms for releasing prefabricated components of spring contact elements from the sacrificial substrates. Many of the processes, metallurgies and mechanisms disclosed therein are directly applicable to the methods and apparatus of the present invention.
Commonly-owned, co-pending U.S. patent application Ser. No. 08/802,054 filed Feb. 18, 1997 discloses a technique for making microelectronic contact structures by masking and etching grooves into a sacrificial substrate (e.g., a silicon wafer), then depositing one or more layers of metallic material into the grooves, then transferring the resulting structures onto an electronic component such as by brazing, then removing the sacrificial substrate so that the fabricated structures are secured at one end to the electronic component and have another end for contacting another electronic component and function as spring contact elements. The present invention takes the concept a step further, providing an alternate technique for fabricating such spring contact elements and mounting them to terminals of electronic components.
Commonly-owned U.S. Pat. No. 6,184,053 discloses a technique for making microelectronic contact structures by applying a series of masking layers patterned with openings onto a substrate such as a semiconductor device, then depositing one or more layers of metallic material into the openings, then removing the masking layers. This results in a plurality of spring contact elements having been fabricated on the substrate at lithographically-defined locations.
The present invention addresses and is particularly well-suited to making interconnections to modern microelectronic devices having their terminals (bond pads) disposed at a fine-pitch. The invention is useful for devices with arbitrarily large pitch, but also is particularly useful for fine pitch. As used herein, the term xe2x80x9cfine-pitchxe2x80x9d refers to microelectronic devices that have their terminals disposed at a spacing of less than 5 mils, such as 2.5 mils or 65 xcexcm. As will be evident from the description that follows, this is preferably achieved by taking advantage of the close tolerances that readily can be realized by using lithographic rather than mechanical techniques to fabricate the contact elements.
An exemplary application for making fine-pitch pressure connections between electronic components can be found in commonly-owned U.S. Pat. No. 5,974,662, which discloses a probe card assembly including elongate resilient (spring) contact elements mounted to a xe2x80x9cspace transformerxe2x80x9d component. As used herein, a space transformer is a multilayer interconnection substrate having terminals disposed at a first pitch on a one surface thereof and having corresponding terminals disposed at a second pitch on an opposite surface thereof, and is used to effect xe2x80x9cpitch-spreadingxe2x80x9d from the first pitch to the second pitch. In use, the free ends (tips) of the elongate spring contact elements make pressure connections with corresponding terminals on an electronic component being probed (e.g., tested).
Another example of an application for fine pitch spring contact elements can be found in commonly-owned U.S. Pat. No. 6,064,213, which discloses mounting springs on active semiconductor devices.
An object of the present invention is to provide an improved technique for fabricating microelectronic contact structures, such as spring contact elements.
Another object of the invention is to provide a technique for fabricating microelectronic contact structures, such as spring contact elements, using processes that are inherently well-suited to the fine-pitch, close-tolerance world of microelectronics.
Another object of the invention is to provide a technique for fabricating microelectronic contact structures, such as spring contact elements, that are suitable for probing electronic components such as semiconductor devices, and that is readily scaleable to probing fine-pitch peripheral interconnect structures.
Another object of the invention is to provide a technique for fabricating microelectronic contact structures, such as spring contact elements, that are suitable for socketing electronic components such as semiconductor devices, such as for performing burn-in on said devices.
According to the invention, microelectronic contact structures are fabricated by forming various portions (xe2x80x9ccomponentsxe2x80x9d) thereof on a corresponding number of sacrificial substrates, then joining the portions to an electronic component and to one another.
Each contact structure has three portions (components): a base end portion or xe2x80x9cpostxe2x80x9d component, a middle portion or xe2x80x9cbeamxe2x80x9d component, and a contact end portion or xe2x80x9ctipxe2x80x9d component. The contact structure is useful for making an electrical connection with a terminal of another electronic component, whether by pure pressure connection or by soldering thereto.
For example, for a plurality of contact structures:
(a) The post components of a plurality of contact structures are formed on a one sacrificial substrate, at prescribed spacing from one another which may, for example, correspond to the terminal layout of an electronic component. The post components can then be joined to the terminals (e.g.) of the electronic component. Alternatively, a post component can be fabricated directly on the electronic component.
(b) The beam components of the plurality of contact structures preferably are elongate, each having two opposite ends and two opposite surfaces. One or more beam components are formed on a sacrificial substrate, at prescribed spacing from one another corresponding to the layout of the post components on the electronic component. A beam component can then be joined, such as by one of its ends and by one of its surfaces, to a corresponding post component. A group of beam components can be joined as a group to a corresponding group of post components.
(c) The tip components of the plurality of contact structures are formed on another sacrificial substrate, at prescribed spacing from one another, preferably corresponding to the terminal layout of another electronic component which is to be contacted by the contact structures. A tip component can then be joined to a corresponding beam component at a position along the beam component which is offset from the post component to which the beam component is joined. The tip component may be joined to an opposite (from the post component) end of the beam component, and may be joined to an opposite (from the post component) surface of the beam component. A group of tip components can be joined as a group to a corresponding group of beam components.
In an embodiment of the invention, the post, beam and tip components of each contact structure are fabricated by applying a patterned masking layer onto a sacrificial substrate, the masking layer having openings extending through to the sacrificial substrate, then depositing one or more layers of metallic material into the openings. The openings in the masking layer are at positions whereat it is desired to fabricate the respective component of the contact structures, and define the geometry (shape) of the respective component of the contact structures. A plurality of contact structures may be fabricated in this manner on the sacrificial substrates, with lithographically-defined tolerances (e.g., dimensions, spacing, alignment).
According to an aspect of the invention, a sacrificial substrate may be provided with a release mechanism which may be a dissolvable layer such as aluminum or multiple metallic layers, either of which will permit the components of the contact structures to be released from the respective sacrificial substrate upon which they are fabricated.
An exemplary sacrificial substrate upon which the components of the contact structures may be fabricated is a silicon wafer, in which case the process of the present invention advantageously utilizes the directionally selective etching of silicon (as, for example, used for micro-machining processes) to create an electroform which is used to plate up the components of the contact structures. This approach may optionally employ laser-based ablation of photoresist, as opposed to lithographic development of the photoresist, in order to create the high aspect ratio of width to height which is preferred for fine pitch spacing between the contact structures.
The post, beam and tip components of the contact structures are suitably formed of at least one layer of a metallic material. In the case of the post components, the metallic material(s) should preferably have good rigidity (high yield strength) and be suitable for being joined, such as by brazing or soldering, with respective ones of the beam components. In the case of the beam components, the metallic material(s) should be appropriate to permit the resulting contact structure to function, in use, as a spring contact element (i.e., exhibit elastic deformation) when force is applied to its (free) end, and should be suitable for being joined with respective ones of the post and tip components.
In the case of the tip components, the metallic material(s) should have good electrical contact characteristics, and should be suitable for being joined with respective ones of the beam components. All of the post, beam and tip components should include at least one layer which is a good conductor of electricity. It is desirable that the overall contact structure (which may be a spring contact element) be a good electrical conductor.
In the main hereinafter, microelectronic contact structures which are spring contact elements are discussed. However, the present invention is not limited to contact structures which are spring contact elements. Contact structures having more, or less, rigidity than would be required to function usefully as spring contact elements are within the scope of the present invention.
An exemplary contact structure formed in this manner has a length xe2x80x9cLxe2x80x9d between its base (post) end and its contact (tip) end. The base end is preferably offset in a first direction from a central (beam) portion of the contact structure, and the contact end is preferably offset in an opposite direction from the central portion. In this manner, the overall contact structure base end is mounted to a terminal of an electronic component, the beam portion is offset from the electronic component and its contact end is further offset, extending well away from the surface of the electronic component to which it is mounted.
In one particularly preferred embodiment, the resulting contact structure is preferably xe2x80x9clong and lowxe2x80x9d, having:
a length xe2x80x9cLxe2x80x9d, as measured from one end to another end;
a height xe2x80x9cHxe2x80x9d measured transverse the length in a direction that is normal (z-axis) to the surface of the sacrificial substrate (and typically normal to the component to which the contact structure is ultimately mounted);
a contact end (tip) portion which is offset in a one direction (e.g., negative along the z-axis) from a central (beam) portion of the spring element by a distance xe2x80x9cd1xe2x80x9d; and
a base end (post) portion which is offset in one direction (e.g., positive z-axis) from the central (beam) portion of the spring element by a distance xe2x80x9cd2xe2x80x9d.
The beam portion of the contact structure is preferably tapered from the one (base) end to the other (contact) end thereof, the contact structure having the following dimensions:
a width xe2x80x9cw1xe2x80x9d at its base end as measured parallel to the surface of the sacrificial substrate and transverse to the longitudinal axis of the spring element;
a width xe2x80x9cw2xe2x80x9d at its contact end as measured parallel to the surface of the sacrificial substrate and transverse to the longitudinal axis of the spring element;
a thickness xe2x80x9ct1xe2x80x9d at its base end, measured along the z-axis; and
a thickness xe2x80x9ct2xe2x80x9d at its contact end, measured along the z-axis;
resulting in:
a widthwise taper angle xe2x80x9cxcex1xe2x80x9d (alpha); and
a thickness taper angle xe2x80x9cxcex2xe2x80x9d (beta).
The tip portion of the contact structure is also suitably provided with a projecting tip feature, said tip feature having a dimension xe2x80x9cd3xe2x80x9d measured along the z-axis.
There is thus described herein an exemplary contact structure suitable for effecting connections between two electronic components, typically being mounted by its base (post) end to a one of the two electronic components and effecting a pressure connection with its contact (tip) end (e.g., by the projecting tip feature) to an other of the two electronic components, having the following dimensions (in mils, unless otherwise specified):
These dimensions are illustrative, and are not meant to limit in any way the scope of the claims. Dimensions outside these ranges may be useful according to various choices readily made by one skilled in the art.
Other objects, features and advantages of the invention will become apparent in light of the following description thereof.